This invention relates generally to line cathodes for flat panel display devices and particularly to such a cathode having localized areas of electron emissive material and a method of making same.
U.S. Pat. No. 4,100,449 discloses a line cathode which is intended for use in a flat panel display device. The cathode includes a line filament, which preferably is tungsten. The tungsten filament is coated with a layer of electron-emissive material along the entire length and uniformly about the filament. In the operation of the cathode, the tungsten filament serves as a heater which causes electrons to be emitted from the emissive coating by the passage of current through the filament. Accordingly, the entire length of the cathode emits electrons without regard to whether or not electron emission is desirable along the entire length.
U.S. Pat. No. 4,199,705 discloses a modulator structure for use in flat panel display devices employing line cathodes of the type disclosed in the aforereferenced patent. The modulator structure includes modulation electrodes arranged in pairs which span the line cathode. Electron emission is desired from the cathode portions between the modulation electrodes so that the electrons are injected into beam guide structures for propagation along channels which compose the display device. The beam guide structures include columns of apertures along which the electron beams propagate. Accordingly, for a color flat panel display device three beams, one for each of the primary colors, are propagated along each of the channels. Electron emission is not needed, or desired, between the columns of apertures and, therefore, the modulator structure includes pairs of isolation electrodes arranged between the pairs of modulation electrodes. The isolation electrodes are voltage biased to hold the portions of the line cathode between the pairs of isolation electrodes in a cut-off mode so that electrons are not emitted into the beam guide structures between the columns of apertures.
Because electron emission is not desired between the columns of beam guide apertures, any structure which minimizes the emission of electrons in these areas would be highly desirable. The instant invention fulfills this need by the provision of a line cathode which is coated with electron emissive material only in the localized areas where electron emission is desired.